Effects of core-shell polycarboxylate superplasticizer on the fluidity and hydration behavior of cement paste

摘要

Polycarboxylate superplasticizer nanomicelles (nano-PCEs) with a core-shell structure were prepared via aqueous emulsion copolymerization in one pot. The shells are constructed with hydrophilic segments of poly(acrylic acid)-co-poly(isobutenyl polyethenoxy ether) (PAA-co-PHPEG), offering the water-reducing performance and stability for nano-PCEs. The cores are self-assembled with hydrophobic segments of polystyrene-co-poly(hydroxyethyl acrylate) (PS-co-PHEA), endowing nano-PCEs with good loss resistant of fluidity for cement pastes. The chemical structure of nano-PCEs was verified by the nuclear magnetic resonance spectrum (H-1 NMR) and fourier transform infrared spectroscopy (FTIR), and the 16 - 48 nm diameter of nano-PCE nanomicelles was determined by dynamic laser scattering (DLS) and transmission electron microscopy (TEM). Compared with comb PCEs, the cement paste containing nano-PCEs exhibited better fluidity retention of three hours by minislump measurements, lower hydration heat and more delayed hydration heat evolution by isothermal calorimetry tests. Furthermore, the hydrolysis and adsorption behavior of nano-PCEs in alkaline cement pastes were deduced, and a working mechanism of nano-PCEs was theoretically explained. This new type of superplasticizer nanomicelles can be used as a long time rheology modifying agent in fresh cementitious systems.